1. Technical Field
The present invention relates to functional elements, sensor elements, electronic apparatus, and methods for producing a functional element.
2. Related Art
As a functional element, a physical quantity sensor element having a fixedly-disposed fixed electrode and a movable electrode which is a movable element section, the movable electrode provided in such a way as to face the fixed electrode with a clearance left between the fixed electrode and the movable electrode and to be able to be displaced, the physical quantity sensor element detecting physical quantities such as acceleration and angular velocity based on the capacitance between the fixed electrode and the movable electrode, has been known (see Japanese Patent No. 4238437 (Patent Document 1) and JP-T-2002-510139 (Patent Document 2)). The physical quantity sensor elements of Patent Document 1 and Patent Document 2 have a structure in which comb electrode sections are mechanically connected to each other while being electrically insulated from each other by a groove filled with an insulating material so that capacitive detection can be performed in a differential manner.
For example, the physical quantity sensor element described in Patent Document 1 uses a single-layer semiconductor substrate or an SOI substrate, and the fixed electrode and the movable electrode each have a plurality of electrode fingers arranged to form the shape of a comb and are disposed in such a way as to mesh with each other.
Moreover, in the physical quantity sensor element described in Patent Document 1, between two electrode fingers, which are located next to each other, of the movable electrode, two electrode fingers of the fixed electrode are provided in such a way as to face each other, and the electrode fingers of the fixed electrode are electrically insulated from each other. This makes it possible to measure independently the capacitance between one of the two electrode fingers of the fixed electrode and the electrode finger of the movable electrode, the electrode finger facing the one electrode finger of the fixed electrode, and the capacitance between the other electrode finger of the fixed electrode and the electrode finger of the movable electrode, the electrode finger facing the other electrode finger of the fixed electrode, and detect physical quantities based on measurement results thus obtained (by using a so-called differential detection method).
Furthermore, in Patent Document 1 and Patent Document 2, the physical quantity sensor element is formed by performing dry etching etc. on the single-layer semiconductor substrate to form a cavity below a movable structure. By using such a method, it is possible to form a sensor structure including an isolated structure by using only a single-layer substrate and prevent a production process from becoming complicated.
However, in Patent Document 1 and Patent Document 2, since a structure in which the isolated movable structure is suspended in the air by forming the cavity by the dry etching etc. in the single-layer semiconductor substrate is adopted, there are restrictions on the thickness and shape of the movable structure, which makes it difficult to achieve higher sensitivity and increased impact resistance.
In particular, in the physical quantity sensor element described in Patent Document 1, the electrode fingers have to be isolated individually so that the fixed electrode and the movable electrode are not brought into conduction, which reduces production efficiency. Furthermore, the SOI substrate is generally expensive, resulting in an increase in cost.